Re: [PATCH 03/10] dir.c: accept a directory as part of cone-mode patterns

> On Tue, Apr 13, 2021 at 7:01 AM Derrick Stolee via GitGitGadget
> <gitgitgadget@gmail.com> wrote:
>>
>> From: Derrick Stolee <dstolee@microsoft.com>
>>
>> When we have sparse directory entries in the index, we want to compare
>> that directory against sparse-checkout patterns. Those pattern matching
>> algorithms are built expecting a file path, not a directory path. This
>> is especially important in the "cone mode" patterns which will match
>> files that exist within the "parent directories" as well as the
>> recursive directory matches.
>>
>> If path_matches_pattern_list() is given a directory, we can add a fake
>> filename ("-") to the directory and get the same results as before,
>> assuming we are in cone mode. Since sparse index requires cone mode
>> patterns, this is an acceptable assumption.
> 
> Makes sense; thanks for the good description.
> 
>> Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
>> ---
>>  dir.c | 5 +++++
>>  1 file changed, 5 insertions(+)
>>
>> diff --git a/dir.c b/dir.c
>> index 166238e79f52..57e22e605cec 100644
>> --- a/dir.c
>> +++ b/dir.c
>> @@ -1378,6 +1378,11 @@ enum pattern_match_result path_matches_pattern_list(
>>         strbuf_addch(&parent_pathname, '/');
>>         strbuf_add(&parent_pathname, pathname, pathlen);
>>
>> +       /* Directory requests should be added as if they are a file */
> 
> "added" or "matched"?  Also, the description seems a bit brief and
> likely to surprise; I'd at least want to expand "file" to "file within
> their given directory" but it might be nice to get some summarized
> version of the commit message or at least state that "-" is just a
> random simple name within the given directory.

>> +       if (parent_pathname.len > 1 &&
> 
> Is this line...
> 
>> +           parent_pathname.buf[parent_pathname.len - 1] == '/')
> 
> to prevent an out-of-bounds indexing?  If so, shouldn't it be "> 0" or
> ">= 1" rather than "> 1"?  And if so, doesn't the strbuf_addch() call
> above ensure the condition is always met?
> 
> Or are we trying to avoid adding the "-" when we parent_pathname is
> just a plain "/"?

> 
>> +               strbuf_add(&parent_pathname, "-", 1);
>> +
> 
> Sorry for all the questions on such a tiny change.  It makes sense to
> me, I'm just curious whether it'll confuse future code readers.